Method of automatically adjusting exposure in a shutterless digital camera

ABSTRACT

In accordance with the present invention a shutterless single lens digital still camera includes an internal processor and auto exposure algorithm that automatically adjusts the exposure of the camera in high and low ambient lighting conditions. The auto exposure algorithm causes the camera to generate a signature of a current ambient luminance level and then in response to the signature to generate automatically an exposure setting.

TECHNICAL FIELD

[0001] The present invention relates to a digital photography system andmethod of using the system to provide electronic still photographs. Theinvention more particularly relates to a shutterless single lens digitalstill camera and method of automatically adjusting the exposure of thecamera in high and low ambient lighting conditions.

BACKGROUND OF THE INVENTION

[0002] With the advent of small low cost digital storage devices,digital still cameras are rapidly replacing silver halide film camerasas the camera of choice. In this regard, such low cost digital storagedevices are enabling digital cameras to provide high resolutionelectronic still photographs. Moreover, with the current improvements inink jet and laser printer technologies, inks, paper, and imagereproduction processes are allowing color prints to be generated fromcaptured digital images that are of substantially the same quality asthat provided through silver halide color prints.

[0003] While digital still cameras have been replacing silver halidecolor print cameras as the preferred choice of the consumer, one of thebiggest drawbacks with most, if not all digital cameras, has been size.That is, in order for a user to capture and review an electronic stillimage such digital devices have incorporated large, bulky and expensiveliquid crystal display units and other light converting devices, such ascharge coupled devices and the like. More particularly, in order for auser to preview an image to captured, the digital camera must givefeedback to a user of what area of a scene to be photographed will becaptured when a picture is taken. This has traditionally beenaccomplished using a built-in device called an optical viewfinder oroptical window that enables the user to visualize the scene and seeexactly what area of the scene that will be captured by the camera lenssystem. The ability of providing an accurate representation of the imageto be capture has been implemented in two different manners between whatis known in the state of the art as a through the lens (TTL) camera anda point and shoot (PAS) camera.

[0004] In the TTL camera, as a user views a scene to be photographed, heor she utilizes the camera viewfinder. More particularly, the user isviewing the scene through the lens system of the camera. That is, withthe help of an internally positioned mirror within the TTL camera, thelight passing through the lens system is reflected by the internalmirror and directed to the optical viewfinder for consideration by theuser. When the user is satisfied with the scene to be captured, themirror is repositioned allowing a direct light path to thephotosensitive plane of the camera, and thus, allowing the scene to becaptured as viewed through the optical viewfinder.

[0005] The PAS camera is much less expensive and does not allow the userto view the scene through the primary lens system. Instead, the opticalviewfinder is provided with a secondary lens system that moves in andout in tandem with the primary lens system. In short then, in the PSAcamera two separate light paths are established; one light path for theprimary lens system to the photosensitive plane of the camera andanother light path through the secondary lens system to the viewfinderfor the scene preview benefit of the user.

[0006] In either implementation whether TTL or PAS, once the user hascaptured the image, the user can then only view the captured image byswitching the camera mode of operation from a preview mode of operationto a review mode of operation. The change in the mode of operationpermits the user to view the previously stored captured images on aliquid crystal display panel of the camera

[0007] Therefore it would be highly desirable to have a new and improveddigital camera that would permit the user to immediately view a capturedimage without switching the mode of camera operation and without theneed of viewing the image on an externally mounted liquid crystaldisplay device.

SUMMARY OF THE INVENTION

[0008] In accordance with the present invention, a shutterless singlelens digital still camera includes an internal processor and autoexposure algorithm that automatically adjusts the exposure of the camerain high and low ambient lighting conditions. The auto exposure algorithmcauses the camera to generate a signature of a current ambient luminancelevel and then in response to the signature to generate automatically anexposure setting.

BRIEF DESCRIPTION OF DRAWINGS

[0009] The above-mentioned features of this invention and the manner ofattaining them will become apparent, and the invention itself will bebest understood by reference to the following description of theembodiment of the invention in conjunction with the accompanyingdrawings wherein:

[0010]FIG. 1 is a pictorial view of a shutterless digital camera whichis constructed in accordance with the present invention;

[0011]FIG. 2 is a diagrammatic top plane view of the camera of FIG. 1,illustrating a through the lens optical path for previewing an image tobe captured;

[0012]FIG. 3 is a diagrammatic side plane view of the camera of FIG. 1,illustrating a through the mirror optical path for facilitating theautomatic setting of camera operating conditions;

[0013]FIG. 4 is a front plane view of the camera of FIG. 1;

[0014]FIG. 5 is another diagrammatic top plane view of the camera ofFIG. 1, illustrating another optical path for facilitating the viewingof a captured digital image;

[0015]FIG. 6 is another diagrammatic side plan view of the camera ofFIG. 1, illustrating another through the lens optical path for capturingan object image;

[0016]FIG. 7 is a block diagram of the operating components of theshutterless digital camera of FIG. 1;

[0017]FIG. 8 is a high level flow chart illustrating control programsteps for capturing an object image with the camera of FIG. 1.

[0018]FIG. 9 is a high level flow chart illustrating control programsteps for automatically setting the focus of the camera of FIG. 1; and

[0019]FIG. 10 is a high level flow chart illustrating control programsteps for automatically adjusting the exposure level of the camera ofFIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] Referring now to the drawings, and more particularly to FIG. 1thereof, there is shown a low-profile, pocket-size shutterless digitalcamera 10 which is constructed in accordance with the present invention.The digital camera 10 is capable of capturing and transmitting desiredones of a plurality of stored digital still images without the use of anexternally visible display device.

[0021] Considering now the digital camera 10 in greater detail withreference to FIGS. 1-6, the digital camera 10 generally includes a lowprofile compact housing 12 that is sufficiently small to fit within ashirt or blouse pocket of a user (not shown). The housing 12 isgenerally rectangular in shape having disposed therein an operatingsystem compartment 14 and a power supply or battery compartment 16. Theoperating system compartment 14 encloses and supports the operativecomponents of the camera 10 in a conventional manner, while the batterycompartment 16 encloses and supports a pair of rechargeable batteries 18and 19 for providing the camera components with the necessary electricalenergy to facilitate normal camera operations.

[0022] In order to capture a desired object image or scene, the camera10 includes a shutterless image capture system 20 and a primary lenssystem 22 that is at least partially disposed in a primary light path 30within the operating system compartment 14. A micro processor controlledmirror system 21, as best seen in FIG. 7, directs light along aplurality of different light paths within the camera 10 to facilitateboth image capture, via an image sensor 34 and image review, via aninternally mounted micro display 44 during the same camera operation aswill be explained hereinafter in greater detail.

[0023] As best seen in FIG. 3, the primary lens system 22 includes aprimary lens 24 mounted at about a forward sidewall of the housing 12and a pair of internally mounted movable focusing lens 25 and 26respectively. The focusing lens 25 and 26 are independently moveablealong a portion of the primary light path 30 to cooperate with theprimary lens 24 for helping to automatically focus light reflecting froman object into the image sensor 34 forming part of the shutterless imagecapture system 20. A fixedly mounted mirror 32 disposed in the primarylight path 30 directs light traveling along the primary light path 30downwardly along an image capture path 40 into the image sensor 34. Inthe preferred embodiment of the present invention, the image sensor 34is a CMOS sensor. It will be understood however, by those skilled in theart that other types and kinds of image sensors, such as a chargecoupled device, can also be utilized for light converting purposes.

[0024] The shutterless image capture system 20 also includes amicroprocessor 36 having coupled thereto the image sensor 34, and a highdensity storage device 38. The micro processor 36 under the control ofan image capture algorithm 600 and an automatic focus algorithm 800control the mirror system 21 and the focusing lens 25 and 26 to providea user of the camera 10 with clear sharp optical and digital images aswill be explained hereinafter in greater detail. As mentioned earlier,the image sensor 34 is preferably in the form of a CMOS device, forconverting light traveling along the image capture path 40 into anelectrical signal indicative of the object image.

[0025] Considering now the mirror system 21 in greater detail withreference to FIGS. 2 and 5, the mirror system 21 generally includes apivotally mounted partially reflective, partially transmissive mirror 42that is mounted in the primary light path 30 between the image sensor 34and the focusing lens 25 and 26. The mirror 42 attenuates the lighttraveling to the image sensor 34 to prevent over driving the imagesensor 34 for image capture purposes but does not sufficiently attenuatethe light traveling to the image sensor 34 to prevent the automaticadjustment of exposure settings for current ambient light conditions viaan auto exposure subroutine 700. In this regard, if the ambient lightconditions are insufficient to activate the automatic exposure featureof the camera 10, the microprocessor 36 will cause the mirror 42 to bepivoted out of the primary light path 30 allowing the light travelingalong the image capture path 40 to reach the image sensor 34 without thelight being attenuated. More particularly, the microprocessor 36 underthe control of the automatic exposure algorithm 800 adjusts the exposuresettings for the camera 10 and then, either before or after deflectingthe mirror 42 from the primary light path 30 permits the image sensor 34to capture the desired object image. In this regard, the camera 10 is atrue shutterless camera as the light sensitive sensor 34 is alwaysreceiving light through the primary lens system 22.

[0026] The digital camera 10 further comprises an optical viewfindersystem 42 (FIG. 7) that includes a micro display 44 and a secondary lenssystem 43 for gathering and focusing light emanating from the object tobe captured or from the digital image of the captured object via themicro display 44. A path selecting mirror 46 forming part of the mirrorsystem 21, is mounted in a through-the-lens light path 50 for eitherindependent or simultaneous movement with the partially reflectivepartially transmissive mirror 42. In this regard, the path selectingmirror 46 is mounted within the operating system compartment 14 in thethrough-the-lens light path 50 that intercepts the light traveling alongthe primary light path 30 after the light has been deflected into thethrough-the-lens light path 50 via the partially reflective partiallytransmissive mirror 42. The mirrors 42 and 46 operate under the controlof the microprocessor 36 to permit a user to either preview an objectimage to be captured via the through-the-lens light path 50 or review acaptured object image via a review light path 60. In short then, theoptical viewfinder system 42 under the control of the microprocessor 36selectively permits a user to visualize either an object or scene to becaptured or alternatively, once an object image or scene is captured, tovisualize the captured object or scene through the viewfinder system 42without the use of an externally visible display device.

[0027] In order to permit the user to focus the camera 10 for the eye ofthe user relative to previewing and reviewing an object image, thesecondary lens system 43 includes a secondary set of lenses, indicatedgenerally at 61 and a redirecting mirror 62 for causing light from theobject image or the micro display 44 to be focused into a housingmounted diopter 64 having a rim adjustor 66. The rim adjustor 66 rotatesunder the control of the user to change or adjusts the focus of theoptical viewfinder system 42 so that either a captured image displayedon the micro display 44 or a through-the-lens object image beingpreviewed prior to capture appears “in focus” to the eye of the user.

[0028] The camera 10 also includes a strobe flash, indicated generallyat 74, to facilitate illuminating an object image under low ambientlight conditions. The strobe flash 74 responds to a flash on/off signalcoupled from a flash on/off switch 78 forming part of a group 68 ofexternal control switches.

[0029] As best seen in FIG. 2, the camera 10 further includes auniversal system bus (USB) or jack 28 that is disposed in a jackcompartment 15 located adjacent to the battery compartment 16. The jackcompartment 15 is accessible via a jack compartment door 54 that ismounted to the camera housing 12 by a set of internal hinge members 56and 58 respectively. The internal hinge members 56 and 58 are disposedin such a manner to permit the jack compartment door 54 to freely openwithout displacing the camera housing 12 from a normally horizontalplane orientation when the underside or bottom of the camera 10 isresting on a supporting surface.

[0030] The digital camera 10 also includes a user interface arrangement67 that includes the group 68 of external control switches and a statusdisplay unit 72 in the form of a flat panel liquid crystal display. Thegroup 68 of control switches are coupled to the microprocessor 36 via aswitch input/output buffering device 69 (FIG. 7) and input/output busindicated generally at 80.

[0031] As best seen in FIG. 1, the status display 72, and the group 68of switches, are housing mounted for easy viewing and manipulation by auser. In this regard, the user interface arrangement 67 helps a user tocontrol camera operations in a fast and convenient manner using agraphical user interface generated by the micro processor 36 and acontrol program 100 that includes the capture image algorithm 700. Thecontrol program 100 as will be explained hereinafter in greater detail,controls camera operations including power on/off, menu selections,flash on/off, zoom in, zoom out, scroll forward, scroll backward and setself time mode. It should be noted that the status display unit 72mounted in a top side of the camera 10 for external viewing by the user,permits the user to view alphanumeric and graphical information only. Inthis regard, the status display unit 72 does not display either objectimages to be captured or captured object images. Instead the statusdisplay unit 72 is only utilized too provide the user with a visualindication of various ones of the camera operating conditions, such asfor example, a camera power on/off indication or a flash mode selectedindication.

[0032] A complete list of the user interface control switches and theirassociated functions are provided in Table 1. TABLE 1 Manually OperableSwitch Function Power On/ Pushbutton 82 to power camera 10 On and Off.Power Off Capture A two-position pushbutton 84 to capture an objectimage. Object Image Scroll Up/ Pushbutton 86 operates to scroll upthrough a group of Zoom Out captured images or through a menu selectiondisplayed on the micro display 52 when the camera 10 is operated in amenu mode. When the camera 10 is operating in a capture image mode,pushbutton 86 functions as a zoom out switch while depressed. ScrollDown/ Pushbutton 88 operates to scroll down through a group of Zoom Incaptured images or through a menu selection displayed on the microdisplay 52 when the camera 10 is operated in a menu mode. When thecamera 10 is operating in a capture image mode, pushbutton 88 functionsas a zoom in switch while depressed. Strobe Flash Pushbutton 78 to turna strobe flash 74 to a desired On or On/Off Off mode, an automatic mode,a red eye AUTO mode, or a red eye On mode, where the mode selected isdisplayed on the status display unit 72. Menu/Image Pushbutton 76 tocause the micro display 52 to display Mode menu selections. Image ModePushbutton 75 to display captured images when the capture object imagepushbutton 84 is activated and view preview object images when thecapture object image pushbutton 84 is not activated.

[0033] Considering now the operation of the camera 10 in greater detailwith reference to FIGS. 1-6, when a user desires to capture a desiredobject or scene as a digital still image, the user activates the camera10 by depressing the power on/off pushbutton 82. To verify that thecamera 10 is activated the user views the status display 72 for such apower on indication.

[0034] Next the user activates the menu/image mode switch 76 to placethe camera in the image mode of operation. The user may verify this modeof operation by looking through the diaopter 64 to verifythrough-the-lens operation. That is, the user will be able to see anobject or scene to be captured through the viewfinder system 42 via thediaopter 64.

[0035] The user next points the camera 10 at the object to be capturedand depresses the capture image pushbutton 84 half way or to a firststop position. The microprocessor 36 responds to the activation ofpushbutton 84 by executing two algorithms: the auto exposure algorithm700 and an auto focus algorithm 800, which algorithms will be describedhereinafter in greater detail. At this point, it will be sufficient toindicate that the execution of the algorithms 700 and 800 cause theexposure and focus of the camera 10 to be automatically set or adjusted.

[0036] Next the user may desire to change the image to be captured byzooming the camera 10 in or out using the pushbuttons 86 and 88respectively. In this regard, the user releases the capture object imageswitch 84 and activates either pushbutton 86 or pushbutton 88 to acquirea desired image to be captured. When the user is satisfied with theimage to be captured as viewed via the diaopter 64, the user once againdepresses the capture object image switch 84 to the first stop positionpermitting the camera 10 to set the focus and exposure settings for thecamera 10. If the user is satisfied with the image to be captured, theuser simply depresses the capture image pushbutton 84 to its fullydepressed or second stop position.

[0037] When pushbutton 84 is fully activated, the microprocessor 36executes a capture image algorithm 600 that will be describedhereinafter in greater detail. In short however, the algorithm 600causes the pivotally mounted mirror 42 to pivot or swing out of theprimary light path 30, permitting light entering through the primarylens system 22 to be focused onto the image sensor 34. The user is ableto verify the capture operation since the path selection mirror 46simultaneously swings or pivots blocking the through-the-lens path 50and establishing the light path from the diaopter 64 to the microdisplay 44 via the review light path 60. In this regard, the object orscene previously saw by the user switches temporarily to a black image.

[0038] The microprocessor 36 then causes the CMOS image sensor device 34to convert the light focused from the primary lens system 22 into anelectrical signal indicative of the captured object or scene. Once theimage has been captured via the image sensor 34, the micro processor 36causes the captured image to be stored in the storage device 38 in acompressed image format, just as in a JPEG image format.

[0039] When the captured image is stored in the storage device 38, themicroprocessor 36 causes the captured image to be accessed from thestorage device 38 and displayed on the micro display 44. In this regard,the black image being viewed by the user switches to the captured image.In short then, the user is able to immediately view the image capturedto determine whether a desired image was in fact captured. The user thenreleases the capture object image pushbutton 84.

[0040] Upon releasing the captured image pushbutton 84, the microprocessor 36 under control of the capture image algorithm 600, causesthe mirrors 46 and 48 to swing or pivot back to their original positionsonce again permitting the user to view an object of scene to be capturevia the through the lens light path 50. The above described imagecapture process is then repeated a desired number of times or until thestorage device 38 is full whichever occurs sooner.

[0041] Considering now the camera 10 in still greater detail withreference to FIG. 7, when the user depresses the capture object imageswitch 84 to the first stop position, the microprocessor 36 undercontrol of the auto exposure algorithm 700 determines a proper exposuresetting for the image sensor 34. More particularly, when the microprocessor 36 receives an adjust focus signal from the image captureswitch 84 being depressed to the first stop position, the microprocessor36 during a first sampling period T₁ samples the ambient light outputsignal from the image sensor 34. The sampling period T₁ is a shortsampling period as there is no need to sample the entire image to becaptured. Instead, the algorithm 700 is only interested in sampling theintensity of the light entering the camera 10 via the primary light path30 and as attenuated by the mirror 48 before reaching the image sensor34 via the fixed mirror 32 and image capture path 40.

[0042] The microprocessor 36 responds to the ambient light output signalfrom the image sensor 34 by subdividing the signal into a series ofsmaller samples that are then arranged in a desired order, such as amatrix arrangement, strip of contiguous sample areas, or a set ofoverlapping sample areas. In this regard, a binary one is establishedfor a given area if its gray level equals or exceeds a predeterminedluminance level of about N% and a binary zero is established for a givenarea if its gray level is less that the predetermined luminance level ofabout N%. The number N is between about 10 and about 30 for mostexposures settings. A more preferred number N is between about 15 andabout 25, and the most preferred number N is about 18. The binary valuesderived from the individual image areas or sets of image areas are thenutilized to form a pointer that locates a corresponding exposure settingor level to be applied to the image sensor 34 of the camera.

[0043] If the ambient light output signal from the image sensor 34 doesnot exceed a given threshold level, the microprocessor 36 causes themirror 48 to pivot out of the primary light path 30 allowing lightentering the primary lens system 22 to be directly focused on the imagesensor 34 without being attenuated. The steps of subdividing, assigning,and forming are repeated to locate another corresponding exposuresetting or level to be applied to change the gain settings of the imagesensor 34 to achieve a desire exposure level.

[0044] Considering now the camera 10 in still greater detail withreference to FIG. 7, when the user depresses the capture object imageswitch 84 to the first stop position, the microprocessor 36 undercontrol of the auto focus algorithm 800 determines a proper focussetting for the primary lens system 22. More particularly, when themicro processor 36 receives an adjust focus signal from the imagecapture switch 84 being depressed to the first stop position, themicroprocessor 36 during a first sampling period T₁ moves the focus lens26 from an initial hyperfocal position to a full range focusingposition. While the focusing lens 26 is moving, the auto focus algorithm800 causes the micro processor 36 to capture and temporarily store aseries of output signals from the image sensor 34.

[0045] At the end of the sampling period T₁ the micro processor 36 undercontrol of the auto focus algorithm 800 causes the focusing lens 26 toreturn to its initial hyperfocal position during another sampling periodT₂. During the sampling period T₂, the microprocessor 36 under controlof the auto focus algorithm 800 determines which one of the captured andstored image signals is the best focused image. This is accomplished bytaking the derivative of a plurality of lines of pixels in each image,and weighting the center more heavily than the periphery. The image withthe greatest absolute value of derivative is determined to be the imagein the clearest focus.

[0046] If a best focused image is determined during the time period T₂,the microprocessor 36 under control of the auto focus algorithm 800causes the focus lens 26 to move to the best focused position duringanother time period T₃. If the auto focus algorithm 800 did notdetermine a best focused position during the time period T₂, themicroprocessor 36 causes the focus lens 26 to remain in the hyperfocalposition.

[0047] The auto focus position determined by the auto focus algorithm800 will remain set in the camera 10 if the user fully activates thecapture object image switch 84 within a predetermined time period T₄from the end of time period T₃. Stated otherwise, the auto focus featureis disabled and the primary lens system remains set in the last focusposition determined by the auto focus algorithm 800.

[0048] If the user fails to fully activate the capture object imageswitch 84 within the predetermined time period T₄ from the end of timeperiod T₃, the auto focus feature is once again activated and proceedsas described.

[0049] Considering now the viewfinder system 42 in greater detail withreference to FIGS. 2 and 5, the mirror system 21 includes a support arm81 mounted for pivot movement within the housing 12. The support arm 81is coupled to a motor 83 forming part of a motor servo system 96 that isresponsive to the microprocessor 36. The motor servo system 96 and moreparticularly the motor 83 is also coupled the focusing lens 25 and 26respectively to facilitate their movement along the primary light path30 for image focusing purposes. The support arm 81 has mounted at itsdistal end the path selecting mirror 46. In this regard, when thesupport arm 81 pivots about its longitudinal axis, the path selectingmirror 46 is pivotally moved into the through-the-lens light path 50.When the path selecting mirror 46 is so positioned, the viewfindersystem 42 is blocked from observing the light traveling along theprimary light path 30. The path selecting mirror 46 is also sopositioned to permit the viewfinder system 42 to observe lightoriginating from the micro display 44.

[0050] Considering now the image capture system 20 in greater detailwith reference to FIGS. 2, 5 and 7, the image capture system 20 permitsa user to immediately review a captured image once the image has beenstored in the storage device 38. In this regard, the image sensor 34converts light into an electrical signal in the form of a digital signaloutput that is buffered to the micro processor 36 from a buffer memory90 for storage in the storage device 38. The buffer memory 90 forms partof a light converting system 19 that also includes a timing generator 92and gain control circuit 94 to help facilitate the auto focus, autoexposure and image capture features of the camera 10.

[0051] The image capture system 20 also includes a pivotally mountedmechanical linkage 85 that is coupled to the motor 83. The support arm81 has mounted at its distal end the partially reflective partiallytransmissive mirror 42. In this regard, when the mechanical linkage 85pivots from a blocking position to an open position, the mirror 42 ismoved into the through-the-lens light path 50 blocking the viewfindersystem 42 and sufficiently opening the primary light path 30 to permitlight to reach the deflection mirror 32 without being attenuated. In thepreferred mode of operation the mirror 42 and the mirror 46 movesimultaneously. However it should be understood by those skilled in theart that the mirrors 42 and 46 can be moved independently of one anotherto accomplish the same result. Thus for example, under low ambient lightconditions when the user depresses the image capture pushbutton 84 to ahalf way position, the mirrors 42 and 46 remain stationary while theauto exposure and auto focus algorithms 700 and 800 are executed by themicroprocessor 36. In this regard, if there was insufficient ambientlight the capture image routine 600 may delay the moving of the pathselecting mirror 46 when the user fully depresses the pushbutton 84. Inthis situation, the capture image routine 600 first causes the mirror 42to be moved into the through-the-lens path 50 allowing the auto exposurealgorithm 700 to adjust the exposure setting of the camera prior tocapturing the object image. Once the auto exposure subroutine 700 isexecuted, the capture image routine 600 proceeds by capturing the imageand moving the path selecting mirror 46 to permit the user, via theviewfinder system 42, to observe light originating from the microdisplay 44. In this example therefore, the mirrors 42 and 46 moveindependently of one another and not simultaneously as described in thepreferred embodiment of the present invention.

[0052] Considering now the capture image routine 600 in greater detailwith reference to FIG. 8, the capture image routine 600 begins at astart command 602 that is initiated whenever the user depresses theimage capture switch 84 to a half way position. Upon detection of theactivation of the image capture switch 84, the capture image routine 600advances to a decision step 604 to determine whether the user hasdepressed the image capture switch 84 to a fully depressed positionwithin T seconds of the last time the switch 84 was fully depressed. Inthis regard, if the switch 84 has not been fully depressed the routine600 proceeds to a call command 620 that calls the AUTO EXPOSUREsubroutine 700. The auto exposure subroutine 700 will be describedhereinafter in greater detail.

[0053] After the exposure subroutine 700 has been executed at the callstep 620, the program advances to a call step 622 that calls anAUTO-FOCUS subroutine 800. The AUTO-FOCUS subroutine 800 will bedescribed hereinafter in greater detail. Once the AUTO-FOCUS subroutine800 has been executed the program proceeds to a go to command 624 thatcauses the program to go to a command step 606.

[0054] Considering again the decision step 604, if a determination ismade at the decision step 604 that the image capture switch 84 hadpreviously been fully depressed within T seconds, the image captureroutine 600 proceeds to the command step 606 that causes the partiallyreflective partially transmissive mirror 48 to be pivoted out of theprimary light path for t milliseconds. The time period t milliseconds isa sufficient period of time to permit the image sensor 34 to capture thelight indicative of an object image and to convert the captured lightinto an electrical signal indicative of the object image. In thisregard, when the mirror 48 is pivoted out the primary light path andinto the secondary light path blocking the user from seeing the objectimage passing through the primary lens.

[0055] Next, the routine 600 proceeds to a decision step 607 todetermine whether the exposure of the camera 10 was set when the autoexposure subroutine 700 was previously executed. If the exposure of thecamera was not previously set when the mirror 42 was disposed in theprimary light path30, the routine 600 proceeds to the call command 609that calls the auto exposure subroutine 700. When the auto exposuresubroutine 700 has been successfully executed, the subroutine 700 existsto a command step 608.

[0056] Considering again the decision step 607, if the exposure of thecamera 10 was previously set when the mirror 42 was disposed in theprimary light path30, the routine 600 proceeds directly to the commandstep 608 without calling the auto exposure subroutine 700 as previouslydescribed. Command step 608, causes the image sensor 34 to be activatedfor a sufficient period of time to convert the light reflecting from theobject image into a binary electrical signal. Once the binary signalindicative of the object image has been generated by the image sensor34, the routine 600 proceeds to a command step 610 that causes thebinary signal to be stored in the storage system 38. The command 610also causes the path selecting mirror 46 to be pivoted into the throughthe lens or secondary light path 50 to permit the user to view thescreen of the micro display 44.

[0057] When the path selecting mirror 46 has been pivoted into thesecondary light path 50, the routine 600 causes proceeds to a commandstep 612 that causes the object image immediately stored in the storagesystem 38 to be retrieved and transferred to the micro display unit 44.In this manner the user is able to immediately view the captured objectimage without changing the operating mode of the camera from a previewmode to a review mode.

[0058] Next, the routine 600 proceeds to a decision step 614 todetermine whether the user has released the image capture switch 84. Ifthe user has not released the capture switch 84, the program will waitat the decision step 614 until the switch 84 is released. When theswitch 84 is released, the routine advances to a command step 616 thatcauses the mirrors 42 and 46 to be returned to their initial positions.Also at the command step 616 a program timer is activated to facilitatedetermining whether the auto exposure and auto focus algorithms 700 and800 need to be executed again as previously described with reference tothe decision step 604. Once the program timer has been set, the controlprogram 600 proceeds to an end command 618 to exit the routine 600 andwait for the user to once again activate the capture image switch 84.

[0059] Considering now the auto exposure algorithm 700 in greater detailwith reference to FIG. 10, when the auto exposure algorithm 700 iscalled from step 620 (FIG. 6) the auto exposure subroutine advances froma start command 702 to an initiate capture command 704. The initiatecapture command enables the image sensor 34 to generate a exposurecalibration signal indicative of the ambient light conditions seenthrough the primary lens 24. In this regard, the signal generated by theimage sensor 34 is indicative only of a portion of the entire image seenthrough the primary lens 34.

[0060] The subroutine then advances to a subdivide command 706 thatcauses the exposure calibration signal to be subdivided in a pluralityof gray level segments. As each segment is formed, the resulting segmentis stored via an arrange and store command 708. In this regard, thesegments may be stored in a matrix arrangement, a strip of contiguoussegments, or as sets of overlapping segments.

[0061] The subroutine then proceeds to a convert command 710 thatretrieves each segment and assigns each retrieved segment a binaryvalue. A binary one is established for a given segment if its gray levelvalue exceeds a predetermined luminance level of about eighteen percent.If the given segment does not exceed the about eighteen percentthreshold value, the segment is assigned a binary zero value. Theassigning of binary values continues until all segments in thearrangement have been assigned a one or zero value. The assigned valuesare stored via a store command 712 and are subsequently utilized as apointer. The subroutine then advances to a set exposure level command714 where the microprocessor______retrieves an exposure value thatcorresponds to a desired exposure setting based on the determinedpointer value. The retrieved exposure value is applied to the camera 10.The subroutine then goes to a return command 716 that returns control tothe main program at the call command 622 (FIG. 6).

[0062] Considering now the auto focus algorithm 800 in still greaterdetail with reference to FIG. 9, when the auto focus subroutine 800 iscalled from step 622 (FIG. 6) the auto focus subroutine advances from astart command 802 to an initiate capture sequence command 804. Theinitiate capture sequence command 804 causes a sampling period of T₁seconds to be subdivide into a plurality of t₁ sampling periods, tocause a sequence of images to be captured. In this regard, one imagewill be captured and temporarily stored at each t₁ occurrence. Thealgorithm then advances to a command step 806 that causes the primarycamera lens to move from an initial hyperfocal position to a full rangefocusing position during the sampling period T₁. From the foregoing itshould be understood by those skilled in the art that as the primarylens system is moving over its full focusing range a series of imageswith different focus characteristics are being captured.

[0063] The subroutine then proceeds to a determination step 808 todetermine whether the primary lens system has advanced through its fullfocus range. If the lens has not been moved through its full range thesubroutine advances to a command step 810 that causes a current image asviewed through the primary lens to be temporarily stored. The subroutinethen returns to the determination step 808. From the foregoing it shouldbe understood by those skilled in the art that as the primary lenssystem is moving over its full focusing range, different ones of theimages captured are being temporarily stored.

[0064] Once a determination is made that the primary lens has moved overits full range of motion, the subroutine advances from determinationstep 808 to a return lens command 812. The return lens command 812causes the primary lens to be returned to its initial hyperfocalposition.

[0065] After the return command 812 has been executed the subroutineadvances to a calculate command 814 that calculates a focus factor foreach of the temporarily stored images in order to determine which one ofthe captured image has the best focus factor. In this regard, thesubroutine advances to a store command 816 that causes a current focusfactor to be stored if it is indicative of a better focused image thenthat of a previously stored image. The subroutine then goes to adetermination step 818 to determine whether the primary lens hasreturned to its initial hyperfocal position.

[0066] If the primary lens has not returned to its initial hyperfocalposition, the subroutine returns to the calculate step 814 and proceedsas described previously. If the primary lens has returned to its initialhyperfocal position, the subroutine advances to a determination step 820to determine whether a best focused position has been determined. If abest focused position has not been determined, the program advance to areturn step 824 that returns the subroutine to the main control programat the go to step 624 (FIG. 8). If a best focused position has beendetermined, the program advances to a move lens command 822 that causesthe primary lens to move to its best focused position. Once the lens hasbeen moved to a best focused position, the subroutine proceeds to thereturn step 824.

[0067] Considering now the camera 10 in still greater detail withreference to FIG. 7, the status display 72 is mounted in the top side ofthe camera housing 12 for viewing by the camera user. The display 72 ispreferably a liquid crystal display that can display alphanumeric andgraphical information. The display 72 is driven in a conventional mannerby a display driver circuit 70 that will not be described hereinafter ingreater detail. The display driver 70 is coupled to the microprocessor26 via the bus 80 as best seen in FIG. 7.

[0068] The display driver 70 is also coupled to the micro display 44 onwhich the recorded images are displayed each time the user actuates theimage capture switch 84 while the camera 10 is operated in an imagecapture mode of operation. The micro display 44 also displays menuinformation when the camera is operated in a menu mode of operation. Inthis regard, when the camera is operated in the menu mode of operation,the user via the scroll switches 86 and 88 can scroll through the imagesstored in the storage system 38 and view menu selection items for thepurpose of downloading selected ones or all of the stored images via theuniversal system bus 26, or deleting one or all of the stored images. Inshort then, the micro display 44 can display a series of menus providinga plurality of command options that can be selected by the user as partof a graphical user interface (GUi) generated by the microprocessor 36using a control program stored in the internal memory 38.

[0069] The manually actuable controls 86 and 88 may be depressed toscroll up and down through the command options displayed on the microdisplay 44 to provide the GUI. The pushbutton 86 when depressed in themenu mode of operation causes the micro processor 36 under the commandsof the control program stored in the internal memory 38 to selectcommand options that are highlighted on the display screen of the microdisplay 44.

[0070] While preferred embodiments of the present invention have beendescribed and illustrated herein, it should be understood by thoseskilled in the art that the invention may be varied in both arrangementand detail. Therefore, the protection afforded the present inventionshould only be limited in accordance with the claims that follow.

We claim:
 1. A method of automatically setting a camera exposure level,comprising: generating a signature of a current ambient luminance level;and generating an exposure setting in response to said signature.
 2. Amethod of automatically setting a camera exposure level according toclaim 1, wherein said step of generating a signature of a currentambient luminance level includes: capturing an image indicative of saidcurrent ambient luminance level; sub-dividing the image into a pluralityof image areas; determining for each image area whether its currentambient luminance level is about a predetermined gray level; assigningeach image area a binary value indicative of whether a current ambientluminance level associated with a individual image area is about apredetermined Grey level; arranging the assigned binary values into apointer; and following said pointer to an exposure setting levelappropriate for capturing an object image reflecting the current ambientluminance level.
 3. A method of automatically setting a camera exposurelevel according to claim 2, wherein said step of generating an exposuresetting, includes: retrieving said exposure setting level; and setting again level indicative of a desired exposure setting.
 4. A method ofautomatically setting a camera exposure level according to claim 2,wherein said step of sub-dividing the image into a plurality of imageareas includes: arranging said plurality of image areas in a matrix. 5.A method of automatically setting a camera exposure level according toclaim 2, wherein said step of sub-dividing the image into a plurality ofimage areas includes arranging said plurality of image areas into astrip of contiguous image areas.
 6. A method of automatically setting acamera exposure level according to claim 2, wherein said step ofsub-dividing the image into a plurality of image areas includes:arranging said plurality of image areas into sets of overlapping imageareas.
 7. A method of automatically setting a camera exposure levelaccording to claim 6, wherein said sets of overlapping image areas arepaired sets of overlapping image areas.
 8. A method of automaticallysetting a camera exposure level according to claim 2, wherein said stepof capturing includes: passing said image indicative of said currentambient luminance level through a primary lens system, said primary lensbeing disposed in a portion of a primary light path; passing said imageindicative of said current ambient luminance level through a partiallytransmissive and partially reflective mirror, said mirror being disposedin another portion of said primary light path; and converting the imagepassed through said mirror into an indication of said current ambientluminance level.
 9. A method of automatically setting a camera exposurelevel according to claim 8, wherein said set of converting including:establishing a threshold indication; and moving said mirror out of saidprimary light path to permit the image to be converted withoutattenuation by said mirror.
 10. A shutterless digital camera,comprising: shutterless means for capturing a portion of an imageindicative of a current ambient luminance level; signature generatingmeans for generating a signature of said current ambient luminancelevel; and automatic means for generating an exposure setting inresponse to said signature.
 11. A shutterless digital camera accordingto claim 10, wherein said shutterless means includes: capturing means ofconverting light into an electrical signal indicative of said currentambient luminance level; timing means for subdividing said electricalsignal into a plurality of image area signals; determining meansresponsive to individual ones of said plurality of image area signalsfor determining whether each individual image area signal is indicativeof at least a predetermined gray scale luminance level; binary means forassigning a binary one value to an individual one of said image areasignals when the signal is indicative of at least a predetermined grayscale luminance level and for assigning a binary zero value to anindividual one of said image area signals when the signal is notindicative of at least a predetermined gray scale luminance level;pointer means for arranging the assigned binary values into a pointer;and retrieving means responsive to said pointer for retrieving one of aplurality of different exposure setting levels, said one exposuresetting level being an appropriate level for capturing an object imagereflecting said current ambient luminance level.